Rose Darabcsek Abbey Marschel Amelie Sjoblom

1. Glaciers In The United States Rose Darabcsek Abbey Marschel Amelie Sjoblom

2. Overview • Glaciers and polar ice store more water than lakes and rivers, groundwater, and the atmosphere combined. • Ten percent of our world is under ice today, equaling the percent being farmed. • If the world's ice caps thawed completely, sea level would rise enough to inundate half of the world's cities. • Alaska is four percent ice.

3. Glaciers in Alaska History • Columbia Glacier: one of the largest tidewater glaciers in the state, can be viewed from boats departing from Valdez or Whittier. • The Harding Icefield in Kenai Fjords National Park covers 300 square miles. • Portage Glacier: Several hanging glaciers can be observed in the mountains surrounding the community of Girdwood, which is about a 45-minute drive along the Turnagain Arm of Cook Inlet from Anchorage. • Mendenhall Glacier: just north of Juneau, is the most accessible of the glaciers in the 1,500-square-mile Juneau Icefield. • Malaspina Glacier: the largest glacier in the state, with an area of 1,500 square miles and extending 50 miles from Mount St. Elias toward the Gulf of Alaska. • The glaciers seen here today are remnants of a general ice advance- the Little Ice Age- that began about 4,000 years ago. • This advance in no way approached the extent of continental glaciation during Pleistocene time. • The Little Ice Age reached its maximum extent here about 1750, when general melting began.

4. Formation of Glaciers • Glaciers form because snowfall in the high mountains exceeds snowmelt. The snowflakes first change to granular snow, round ice grains, but the accumulating weight soon presses it into solid ice. Eventually, gravity sets the ice mass flowing downslope at up to seven feet per day. • To be termed a glacier, it must be able to flow under its own weight. It will begin to flow if it is at least 30m thick and flows under the influence of gravity. It starts moving when the force exerted by its weight and surface slope overcome the strength of the glacier on its bed.

5. Types of Glaciers • Temperate Glaciers: There is little sea ice, no ice shelves, and no ice sheets. Summer temperatures are higher than 10 degrees C. Precipitation and melting are high. • Subpolar Glaciers: Temperatures are less than 10 degrees C, so there is some summer rain. There is some surface melting. • Polar Glaciers: The only setting which ice shelves presently occur. Summer temperatures are always less than 0 degrees C so there is no summer rain.

6. Icebergs: Pieces of Glacier • Huge icebergs may last a week or more, and they provide perches for bald eagles, cormorants, and gulls. In Alaska, harbor seals are commonly found on icebergs. • Colors betray a berg's nature or origin. White bergs hold many trapped air bubbles. Blue bergs are dense. Greenish-blackish bergs may have calved off glacier bottoms. Dark-striped brown bergs carry morainal rubble from the joining of tributary glaciers or other sources. • How high a berg floats depends upon its size, the ice's density, and the water's density. Bergs may be weighed down, submerged even, by rock and rubble. A modest looking berg may suddenly loom enormous, and endanger small craft, when it rolls over. Keep in mind that what you see is "just the tip of the iceberg."

7. Animal Habitat

8. Evidence of Glacial Movement • These features are those created beneath the ice by the glacier removing rock material and transporting it away. • They can be large scale, such as glacial valleys carved through the mountains, or small scale, such as the tiny striations engraved in pebbles. • When glaciers cut through land they form a U-shape valley as opposed to the V-shape valley created by a river. • Glacier valleys are larger than river valleys, cut much deeper, can be tens of miles wide, and often reach depths of hundreds of meters. • Striations are useful indicators of the direction of glacier movement. Because it is a line, there are two possible directions of movement.

9. Environmental Effects on Glaciers • Glaciers respond to atmospheric changes, such as climatic warming (global warming) or cooling, or change in the amount or type of precipitation. • Glaciers in the marine realm and ice shelves may respond to changes in sea level and changes in ocean circulation. • Increased meltwater or movement of the debris layer, can increase flow rates. • Response of a glacier to changes in the environment is a shift of the equilibrium line. • Glaciers with more ice mass near the equilibrium line will respond more dramatically to change. This is because a climate change will force the equilibrium line to move, so that a different proportion of ice is within the accumulation zone. • In general, the smaller the ice mass, the faster the response to a change in its environment.

10. Plant Succession • The rapid vegetation change following the glacier’s speedy retreat has enabled scientists to map the course of plant succession. • First, the longest stage develops no more than "black crust", a mostly algal, feltlike nap that stabilizes the silt and retains water. • Second, Moss will begin to add more conspicuous tufts. • Thirdly comes fireweed, dryas, alder, and willows. • These alders fix nitrogen in their roots, and drop leaves that add valuable nitrogen to the soil. This enables spruce to take hold and eventually shade out the alder. • Lastly, small and then large trees grow that can survive cold climates, such as spruce and hemlock. A forest has begun. The higher the altitude, the less trees grow.

11. Trees and exit glacier, fall. Kenai Fjords National Park, Alaska, USA.